1. Field of the Invention
The present invention relates to a video editing scheme to be used in playbacking and editing coded video data.
2. Description of the Background Art
In conjunction with the standardization of the video coding scheme such as MPEG, a use of the coded video has been widening, and there is a demand for an editing apparatus which is capable of retrieving a desired scene from the video quickly, processing the coded video in a coded form efficiently, and changing a playback order of the video.
Conventionally, in order to retrieve a desired scene from the non-coded video such as video images, it has been necessary to repeatedly execute operations such as rewinding and fast forwarding operations, so that there has been a problem that a considerable amount of time is required for the scene retrieval. In view of this problem, there has been a proposition of a video editing apparatus as disclosed in Japanese Patent Application Laid Open No. 5-183862 (1993), which has a detection means for detecting images at which the scene is changed in the video, and an index information production means for producing a video index information in terms of icons obtained by reducing the images detected by the detection means. This video editing apparatus has already been developed for practical use. According to this proposition, the icons representing the scene changed images detected from the video are displayed in a form of multiple image field display, so that an outline of the video content can be comprehended without watching the video in a time order, and therefore it becomes possible to realize the scene retrieval efficiently.
This conventional video editing apparatus is designed to handle the non-coded video such as video images, and when this conventional video editing apparatus is directly applied to handle the coded video, the following problems arise.
FIG. 1 shows one exemplary apparatus configuration in which the above described conventional video editing apparatus is directly applied to the coded video.
In FIG. 1, a portion enclosed by a solid line represents a general configuration of a conventional apparatus for playbacking the coded video in which a coded video control unit 22 reads out the coded video data stored in a coded video storage unit 21 and supply the coded video data to a decoding unit 23 which decodes the coded video data. The decoded video data are then supplied to and displayed at a display unit 24. Here, the decoding unit 23 is usually implemented in a form of dedicated hardware.
Also, in FIG. 1, a portion enclosed by a dashed line represents the above described conventional video editing apparatus in which a scene change detection means 25 detects images at which the scene is changed in the video, an index production means 26 produces a video index information in terms of icons obtained by reducing the images detected by the scene change detection means 25, and a display means 27 displays these icons in a form of multiple image field display.
FIG. 1 shows one exemplary configuration for realizing the above described conventional video editing apparatus in combination with an apparatus for playbacking the coded video, in which the decoded video data are taken from the decoding unit 23 of the playback apparatus and entered into the above described conventional video editing apparatus.
However, the decoding unit 23 is usually implemented in a form of dedicated hardware as already mentioned above, so that it is not easy to read out and process the decoded video data by means of software. Even if it is possible, there still remains a problem that an amount of data for the decoded video data is very large so that the data transfer (such as a data transfer using an internal bus of a computer) requires a considerable amount of time.
FIG. 2 shows another exemplary apparatus configuration in which the above described conventional video editing apparatus is directly applied to the coded video.
In FIG. 2, the scene change detection means is provided in a form of coded video data scene change detection means 28 which can detect a scene change directly from the coded video data. Such a coded video data scheme change detection means can be realized by using the known configuration as disclosed in Japanese Patent Application No. 6-22304 (1994). Then, the coded video control unit 22 reads out the coded video data stored in the coded video storage unit 21 and supply the coded video data directly to the coded video data scene change detection means 28 (before supplying the coded video data to the decoding unit 23), so that an index production means 29 produces the index information according to the scene changes detected by the coded video data scene change detection means 28.
This configuration of FIG. 2 has a problem in that the index production means 29 is required to carry out the decoding processing in order to produce the icons in forms of the reduced images, so that a considerable amount of time is required for the index production processing.
In addition, there is another conventionally encountered problem that it is not easy to edit the coded video. This problem stems from the fact that it is not easy to segment the coded video data at arbitrary positions and change an order of segments. Because of this problem, it has conventionally been customary to carry out the editing on an original tape and then the edited video is coded, so as not to require the editing on the coded video,
This problem regarding a difficulty of editing the coded video will now be described in further detail for an exemplary case of using the MPEG coding scheme.
In the MPEG coding scheme, the image sequence is coded by using a combination of an intra-field coded picture (I picture) in which the image is compressed by removing the redundancy within each image field, an inter-field forward direction predictively coded picture (P picture) which utilizes a correlation between an image of interest and a past image, and an inter-field bidirectional predictively coded picture (B picture) which utilizes a correlation among an image of interest, a past image, and a future image, as shown in FIG. 3. In FIG. 3, a picture 31 is an I picture which is coded within an image field, so that it is possible to reproduce an image from the data of this picture 31 alone. On the other hand, a picture 32 is a B picture from which an image cannot be reproduced until its past picture 31 and its future picture 33 are decoded. Consequently, in the MPEG coded video, it is only possible to segment the video at a position of the I picture. If the video is segmented at a position of the B picture 32, for instance, it would become impossible to decode the B picture 32 because data of the I picture 31 would become unavailable.
In other words, in order to segment the video at a portion other than that of the I picture, it would be necessary to reconstruct the coded data by repeatedly executing the decoding processing and the coding processing, and because of that, there has been problems that it would require a considerable amount of time and an image quality would be degraded.
For the same reason, in the MPEG, a position from which the video playback can be started is limited to a position of the I picture (or a top of a packet containing the sequence header that stores parameters necessary for the decoding, strictly speaking). The above described conventional video editing apparatus does not account for this limitation at all, so that when the above described conventional video editing apparatus is directly used to handle the coded video, there is a problem that the decoding unit would not operate properly at a time of the video playback, that is, the playbacked images would be temporarily disturbed until the I picture is displayed. In addition, Japanese Patent Application Laid Open No. 5-183862 mentioned above does not have any teaching directed to a specific editing operation such as a change of playback orders.
Thus because of the lack of considerations for these problems which are specific to the coded video, the prior art has been associated with a problem that a considerable amount of time is required for the production of icons because it is necessary to carry out the decoding processing at a time of producing icons, as well as a problem that the video cannot be playbacked smoothly because the video decoding unit does not operate properly at a time of the video playback.